Electromagnetic switch



E.;J.'MURPHY. ELEQTRQMAGNETIC SWITCH. "APPLICATION man APR. 29. p16.

Patented J une li), 1919.

2 SHEETS-SHEET 1.

Inventor":

Edwin JM rphg, y His N; ornegr E. J. MURPHY.-

ELECTROMAGNETIC SWITCH.

APPHCATION FILED APR.29. ma.

Patenmd June 10, 19 19.

' 2 SHEETSSHEET 2- Inventor";

Edwin J. r-phg, b5

v His a cltorneg.

N i T T ED STATES Enwm J. mourns,

OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL COMPANY, A CORPORATION OFNEW YORK.

PATENT OFFICE.

ELECTROMAGNETIC SWITCH.

. To all whom it may concern Be it known that I, EDWIN J MURPHY, a

. citizen of the United States, residing at and useful Improvements inElectromag- "Schenectady, c'ounty of Schenectady, State of New York,have invented certain new netic Switches, of which the following isaspecification.

My invention relates to means for controlling the circuits of electricmotors and more particularly to improved means whereup to speed. Variousmeans havebeen de- .vised for controlling the operationiof the switchesso that they will only close when the current is at a proper value, thatis, after a switch has operated to cut out a section of resistance ,thenext. switch will not operfate'until the current has dropped to a safevalue due to the speeding up of the motor.

A formof switch which has frequently beenv proposed for'this purpose isone in which a shunt coil closes the'switch and a series coil, insteadof controlling the circuit of the shunt coil, positively prevents theswitch from. closing by actually holding it open, that is, the shuntcoil pulls against the series or holding out coil. A switch of thisgeneral character, is disclosed in" patent to Fraser #655,335. The difliculty with the device shown in this patent is that the value of currentin the holding out winding at which the switch will close de pends uponthe pull of the-shunt coil, which of course will vary with thevoltageand also with the temperature of the coil. In

other words, the setting of the switch, '11. a.

the motor current value at which it closes, changes with change ofvoltage. It also closes at one value of current in the series coil whenthe shunt coil is cold and another when it is at its operatingtemperature,

which is ordinarily about (30 degrees C.

Attempts have been made to overcome this difficulty by having anauxiliary memher, which is operated by the shunt coil,

place a spring under: tension which tends to move the switch member toclosed position. This tendency is opposed by the series Specification ofLetters Patent.

Patented June 10, 1919 Application filed April 29, 1916. Serial No.94,465.

coil when the current is high and when the current drops to apredetermined value, the spring overcomes the pull of the-series coiland closes the switch. .Such' an arrangement is unsatisfactory forithereason'that the switch is closed by a spr ng instead of byelectromagnetic pull, and it is impossible to obtain the requiredpressure between the contacts. The spring weakens as the switch membermoves toward closed position, and the pressing together of the''c'ontacts is accomplished when the spring is weakest. As the partswear, the pressure between the contacts decreases.

' One of the objects of my invention is to improve the electroma eticswitch of the type above described g providin means whereby the switchmember will be operated so as to be positively closed and-wiped home bythe electromagnetic pull of the shunt coil when the current in theseries coil drops to a predetermined value, the arrangement being suchthat the value of current in nnnc'mxc the series coil at which theswitch closes will be independent of the variations in pull of the shuntcoil due to variations in voltage and other causes.

In the accompanying drawing illustrating my invention embodied inconcrete form, Figure 1 is a side elevation of an electromagnetic switchembodying my invention; Fig. 2 is a front elevation of the same; Figs. 3and 4 are diagrannnatic views of the switch showing the parts indifierent positions; Fig. 5 is a diagrammatic view showing my switchesconnected to start a motor, and Figs. 6-10 are similar views of amodified form of my invention.

Referring to the drawing, 10 represents the slate base upon which theparts are mounted. These parts comprise, a stationary contact 11, aswitch member 12 operated byshaped magnet frame 15 having a pole piece16 cooperating with the switch member and The ma etic structure a leg 17to which the switch-member is pivoted at 18.. The switch member isprovided. with the usual contact 19 supported by spring 20 so that thecontactsll and 19 may wipe upon each other as the spring 20 yields in awell understood manner.

In order to prevent the switch member from closing when the current inthe series coil 14 is above a predetenmined value I provide meanswhereby the series coil is opposed by a spring instead of by the shuntcoil, although it is not this spring but the shunt coil which closes theswitch.

1n the particular arrangement shown in the drawing, I provide a lockingmember 21 pivoted at 22 so that when the current in the winding 14 isabove a predetermined value (or for that matter, even when the windingsare de'einergized), it will prevent the closing of the switch member. Asshown a stop finger 23 engages the locking member 21 to prevent theclosing movement of the switch member 12 when the locking member is inthe position shown in the draw ing. This locking member 21 is controlledby a member 24 pivoted at 25 which acts as an armature for the winding14. This armature member is provided with a projection 26 which engagesthe locking member 21. The switch member 12 and the armature member 24are connected by a resilient connection such that when the switch memberstarts to move, it compresses the sprin 27 which tends to force thearmature mem er 2t away from the magnet and trip the locking member. Thearmature member is normally in the position shown in the drawing, thatis, it rests against the pole piece of the magnet 14, it being held inthis position by the weight of the switch member acting through the rod28 extending through the spring 27 having nuts 29 at its lower end asshown which bear against the lug 30 on the armature member. The latch 21is held in the position shown in Figs. 1 and 3 of the'drawing by the pin31.

As thus constructed and arranged, the operationof my device will be asfollows: Normally the parts will be in the position shown in Fig. l ofthe drawing. Assuming that the two windings of the switch are' energizedsimultmieously and the winding l-l energized by a current above thevalue at.

which it is desired that the switch should close, the parts will assumethe posit'on shown in Fig. 3. Referring to this figure it will be seenthat the switch member 12 has been moved slightly until the stop finger23 engages the locking member 21. This causes a certain amount ofcompression of the spring 27 tending to move the armature member 21 onits pivot but this tenden y is resisted by the magnet winding 14. Theshunt-coil is now pulling the switch nrmbcr against the locking memberor latch and the switch member can not close until the latch is tripped.It will also he observed that the tripping of the latch, and thereforethe release of the switch member depends operated line switch forclosing the arma- 'ture circuit and is provided with interlockdeterminedvalue, the armature member will be released and deliver a hammer blow tothe latch 21. The parts-[will now assume the position shown in Fig.4 inwhich it 'will be seen that the latch has been tripped and i the switchmember is positively closed and .75 the contacts wiped home by the shuntcoil. The switch member is therefore positively held open under thecontrol of the current in the series'coil and the variations of ull, inthe shunt coil will have no effect w atso ever upon the value of currentat which the switch member will close.

In Fig. 5, I have shown a diagram of con- .nections for starting anelectric motor in which a plurality of switches of the type abovedescribed are used as resistance switches. Referring to this figure, Are resents the armature and F the shunt fie d of an electric motor. B isan electrically ing contacts C which connect the shunt coils 13 of thevarious resistance switches D, E and F in circuit. In order to effectautomatic progression of these switches, I divide the series coils 14 ofall but the first one to operate into two parts. The arrangement is suchthat when the first switch F closes, a portion of the series winding ofthe next switch is cut out to reduce the num ber of :unpere turns so asto enable the switch to close when the current drops to a predeterminedvalue. Likewise when the econd switch closes, it cuts out a portion ofthe series winding of the next switch.

The operation of this system will now be understood from an ins ectionof Fig. 5. When the line switch B'c oses. the armature circuit iscompleted from the positive side of the line through startingresistances R, R, R and through the series windings 11 to the negativeside of the line. The iuterlocking contact C on the line switch placesall of the shunt coils 14 in circuit across the line. When the currentdrops to the )roper value, the first switch F will close tiereby shortcircuiting resistance R its own series coil 14, and a portion of theseries winding 14 of switch It. When the current again drops to a propervalue, due to the speeding up of the motor, the switch E will close.shortcircuiting resistance R, its own series winding, and a ortion ofthe series winding of switch D. en the current again drops to the propervalue the switchD will close, thereby connectingthe motor directlyacross the line.

Referring to Figs. 6 to 10, it will be seen that I have shown a modifiedarrangement for holding the switch member in open posi- 13!) tion. Inthis case the series coil 14 is pro-- shown is slight,eonipresses.aspring 38 surroundingfr rod 39, one'end of which bears against. jectionon the armature 32-and at'right e link. The rod 39 slides in a proanglesthereto. I The spring 38 is interposed between a shoulder 41 on the rodand the projection 40. When the parts are in their normal positions, thepivot points 33 and 37 are in line with pivot point 42 connecting thelink with the switch arm extension 36.

When a force is applied to the switch arm,

therefore tendingto move it 'to closed position, there is no tendencyfor the armature to move away from the magnet due to the pull of theshunt coil. .Thereis a small initial movement however of the link byreason of the sliding connection with the armature which compresses thespring 38. The reaction of the spring 38 against the projection 40 tendsto force the armature 32 away from its magnet. When the current in thewinding 14 drops to a predetermined value, the spring will overcome themagnet1c pull. The armature will turn on its pivot and throw the pivotpoints out of line so that the shunt coil will close 'the switch, theparts assuming the position shown in Fig. 10. This form of switch may beused in the system shownfin Fig. 5.

It will be seen that I have provided an electromagnetic switch which isclosed by a shunt coil but is held open while the current in the seriescoil is above the predetermined value, the closing point of the switchalways 45 being the same regardless of the variations in pull of theshunt coil.

While I have described my invention as embodying a concrete structureand as operating in a specific manner in accordance with the provisionsof the patent statutes,

it should be understood that I do not limit my invention thereto,sincevarious modifications thereof will suggest themselves to thoseskilled in the art without departing from the spirit of my invention,the scope of which isset forth in the annexed claims.

What I claim as newand desire to secure by Letters Patent of the UnitedStates, is

1. An elcctromagnetic s tch comprising a switch member, an act|lati:;;winding connected to a source of substantially constant potential, and amagnetic structun. lhcrefor for moving the switch member to closedposition, a winding carrying a variable current and means whereby theswitch member is held in open position when the current in the latterwindin is above a predetermined value and is c osed byfthe potentialcoil when the current drops to said value regardless of variations inthe pull of the potential coil.

a switch member, a shunt coil for closing the same, a Winding carrying avariable current,

means for preventing the closure of the switch member whenthe current insaid c 2. An electromagnetic switch comprising winding is high and meansfor releasing the switch member to permit it to be closed by the shuntcoil when the current in the winding drops to a definite value,regardless of variation in the pull of the shunt coil.

3. An electromagnetic switch comprising a switch member, a shunt coilfor closing the same, an electromagnet energized by a variable current,a spring placed under strain by the shunt coil in opposition to the pullof the electromagnet and means including said spring for preventing theclosure of the .switch member when the current in said winding is highand releasing the switch member to permit it to be closed by'the-'mitting it to be closed when the current drops to a definite valuewhich is independent of the pull of the shunt coil.

5. An electromagnetic switch comprising a switch member, a shunt coilfor closing the same, electromagnetic means controlled by a variablecurrent for preventlng closure of the switch member when the current ishigh and a spring opposingthe electromagnetic means and acting torelease the switch member when the current drops to a, definite valuesothat it will be closed by the shunt coil.

6. An electromagnetic switch comprising a. switch member, a shunt coilfor closing the same, electromagnetic means controlled by a variablecurrent for preventing the closure of the switch member when the currentis high, a spring, said means including a movable element which placessaid spring under strain to oppose the electromagnetic means and acts torelease the switch member when the current drops to a definite value sothat it will be eloscd by the shunt coil.

7. An electromagnetic switch comprising sure of the switch member whenthe current is high, a spring held under tension by the magnet and meanscontrolled by said spring whereby when the current drops to a definitevalue a hammer blow 1s delivered which releases the switch member andpermits it to be closed by the shunt coil.

8. An electromagnetic switch comprising a switch member, a shunt coilfor closing the same, electromagnetic means controlled by a variablecurrent for preventing closure of the switch member when the current ishigh, and a spring placed under strain by the shunt coil to oppose theelectromagnetic means and acting to release the switch member when thecurrent drops to a definite value and permit it to be closed by theshunt coil.

9. An electromagnetic switch comprising a switch member, a shunt coilfor closing the same, a spring placed under strain by said coil, andmeans controlled by a variable current for preventing the closure of theswitch member when the current is high comprising a magnetic windingcarrying the variable current, a movable mechanism held against thespring strain, said mechanism operating in response to the springtension when the current drops to a definite value, and per mi-ttingsaid switch member to be closed by the shunt coil.

10. An electromagnetic switch comprising a switch member, an actuatingwinding connected to a source of substantially constant potential, amagnetic structure therefor for moving the switch member to closedposition, a winding carrying a variable current and means whereby theswitch member is normally locked in open position and is held in saidposition when the currentin the latter winding is above a predeterminedvalue and is closed by the potential coil when the current drops to saidvalue regardless of variations in the pull of the potential coil.

It witness whereof, I have hereunto set my hand this 28th day of April,1916.

- EDXVIN J.- MURPHY.

